Tel: +44 (0)1428 661 660



We are the exclusive UK and Ireland distributor for YSI Water Quality Systems for groundwater monitoring applications. YSI is a global business committed to sustaining the quality and viability of the world's water resources with accurate and reliable water quality testing equipment. Their meters have proved to be rugged, reliable, accurate and durable. We include a range in our rental fleet – testament to their true fieldwork credentials.

Please note that BS ISO 11271 requires that all Redox measurements are required to be translated as if they were taken with a SHE electrode (Standard Hydrogen Electrode). A conversion table and a more detailed explanation can be found on our 'Redox Conversion Table', Information Sheet.



Designed for demanding field work the ProDSS is the latest, smartest, most innovative portable water quality multi-parameter instrument from the YSI stable. The ProDSS measures water parameters like dissolved oxygen (optical), pH, ORP, conductivity, specific conductance, salinity, TDS, resistivity, TSS, ammonium, ammonia, chloride, nitrate, depth, temperature and, most importantly turbidity.

YSI has taken the advanced technology from the EXO series to make the new ProDSS the best handheld available. This instrument is rugged and reliable with intelligent, user-replaceable digital sensors that can be connected to any port and that are automatically recognised by the instrument and retain the calibration data.

With optional GPS and depth the ProDSS is completely customisable* and with military specification connectors, IP67 waterproof, rubber over-moulded case and 1-metre drop tests, durability is ensured for longevity of sampling even in the harshest field conditions.

*Rental instruments will be configured/calibrated to measure temperature/conductivity, DO, pH, ORP and turbidity.


The ProDSS is smart, cost-effective and adaptable for the future. Its high-impact body is built to record water quality to depths of 250 meters. The data is stored on-board the instrument for downloading to a laptop on completion of the monitoring sequence.

  • YSI pedigree
  • Real time graph plotting and display
  • Digital instrument with smart sensors that retain calibration status
  • True multi-parameter instrument
  • Single cable
  • Universal ports which can accept any 4 sensors plus depth.
  • Colour display
  • Backlit keypad
  • Optional GPS
  • Rechargeable lithium-ion battery
  • Extensive memory allowing > 100,000 data sets to be saved with site list and data ID tag information
  • 400 GLP (calibration) records
  • Easily transferable data
  • PC program included with the instrument, or backed up to USB memory stick via the built-in, waterproof USB On-The-Go port.
  • Field replaceable sensors
  • Warranty: 3-year instrument; 2-year industry-leading cable assembly and sensors; 1-year pH and pH/ORP sensor modules; 6-months ammonium, nitrate and chloride sensor module
  • Rugged, waterproof military spec connectors
  • Durable enclosure with rubber over-moulded waterproof (IP-67) case
  • Fully backed by the Van Walt Technical team.

Specifications: YSI ProDSS

YSI ProDSS Specifications
Size 8.3 cm width x 21.6 cm length x 5.6 cm depth (3.25 in. x 8.5 in. x 2.21 in.)
Weight with batteries 567 grams (1.25 lbs)
Power Rechargeable lithium-ion battery pack providing ~48 hours of battery life (instrument only with backlight off)
Instrument operating temperature 0 to 50 °C (32 to 122 °F)
Instrument storage temperature 0 to 45 °C (32 to 113 °F) with battery installed; 0 to 60 °C (32 to 140 °F) without battery installed
Display Colour, LCD graphic display
USB port Built-in micro USB On-The-Go port for PC connection, recharging/powering the ProDSS & connecting directly to a USB stick
Cables Available with or without depth sensor in 1, 4, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100-meters
Sensor ports 4 universal sensor ports on each cable; can accept any ProDSS sensor
Warranty 3-year instrument; 2-year bulkhead, cable assembly, and sensors; 1-year pH and pH/ORP sensor modules, ODO sensor caps & Li-ion battery pack; 6-months ammonium, nitrate & chloride sensor modules
Memory > 100000 data sets
Logging modes Single point or continuous with auto-stable feature
GLP compliance Yes; 400 detailed GLP records can be stored & are available to view, download & print.
Languages English, Spanish, Portuguese, French, German, Italian, Japanese, Norwegian, Simplified Chinese, Traditional Chinese
Certifications CE; RoHS; IP-67; WEEE; FCC; UN Part III, Section 38.3, Test methods for lithium-ion batteries (Class 9)
GPS Optional internal GPS; coordinates are stored with measurement data & site lists
Sites & Data ID 100 user-defined sites and 100 user-defined data ID tags
Instrument, Sensor & Cable
Temperature -5 to 70 °C (temperature compensation range for DO mg/L measurement: -5 to 50 °C ) ±0.2 °C 0.1 °C or 0.1 °F (user selectable) °C, °F, K
pH 0 to 14 pH units ±0.2 pH units 0.01 pH units pH, pH mV
ORP -1999 to 1999 mV ±20 mV 0.1 mV mV
Dissolved Oxygen 0 to 500%, 0 to 50 mg/L 0 to 200%: ±1% of reading or 1% saturation, whichever is greater
200 to 500%: ±8% of reading
0 to 20 mg/L: ±0.1 mg/L or 1% of reading, whichever is greater
20 to 50 mg/L: ±8% of reading
0.01 mg/L and 0.1%, or 0.1 mg/L and 1% (user selectable) % saturation, % saturationlocal, mg/L, ppm
Barometer 375 to 825 mmHg ±1.5 mmHg from 0 to 50 °C 0.1 mmHg mmHg, inHg, bar, psi, kPa, atm
Conductivity** 0 to 200 mS/cm 0 - 100 mS/cm: ±0.5% of reading or .001 mS/cm, whichever is greater 100 - 200 mS/cm: ±1.0% of reading 0.001, 0.01 or 0.1 μS/cm (range dependent) μS/cm, mS/cm
Specific Conductance* 0 to 200 mS/cm 0 - 100 mS/cm: ±0.5% of reading or .001 mS/cm, whichever is greater 100 - 200 mS/cm: ±1.0% of reading. User selectable reference temp. (15 to 25 °C; default 25°C) & compensation coefficient (0 to 4%/°C; default 1.91%) 0.001, 0.01, 0.1 mS/cm μS/cm or mS/cm
Salinity* 0 to 70 ppt ±1.0% of reading or ±0.1 ppt, whichever is greater 0.01 ppt ppt or PSU
Total Dissolved Solids* 0 to 100 g/L Calculated from specific conductance and a user-selectable TDS multiplier (0.30 to 1.00; default 0.65) 0.001, 0.01, 0.1 g/L mg/L, g/L, kg/L
Seawater Density* 0.0 to 50.0 sigma, sigma T - 0.1 sigma or sigma T Sigma, Sigma T
Turbidity 0 to 4000 FNU 0 to 999 FNU: 0.3 FNU or ±2% of reading, whichever is greater 1000 to 4000 FNU: ±5% of reading 0.1 FNU FNU, NTU
Total Suspended Solids* 0 to 30000 mg/L User correlated from turbidity field measurements & lab TSS measurements from grab samples 0.01, 0.1 mg/L mg/L
Ammonium***/**** 0 to 200 mg/L NH4 -N ±10% of reading or 2 mg/L, whichever is greater 0.01 mg/L NH4 -N mg/L, NH4 -N mV
Chloride*** 0 to 18000 mg/L Cl ±15% of reading or 5 mg/L, whichever is greater 0.01 mg/L Cl mg/L, Cl mV
Nitrate*** 0 to 200 mg/L NO3 -N ±10% of reading or 2 mg/L, whichever is greater 0.01 mg/L NO3 -N mg/L, NO3 -N mV
Depth 0 to 328 feet (0 to 100 m) ±0.013 ft (±0.004 m) for 1, 4 & 10 m cables ±0.13 ft (±0.04 m) for cables 20 m & longer 0.001 m or 0.01 ft M,ft

*Derived/calculated parameter **Resistivity can be calculated with the conductivity sensor ***ISEs for freshwater only; 20 meter maximum depth ****Ammonia can be calculated and reported from ammonium, temperature, salinity, and p

Instrument, Sensor & Cable
Temperature Thermistor, installed on conductivity sensor Not available 100 m 2 years for conductivity/temperature sensor
pH Combination glass bulb electrode, Ag/AgCl reference electrode with gelled electrolyte 1, 2, or 3 point 100 m 2 years for pH & pH/ORP sensors
1 year for pH & pH/ORP sensor modules
ORP Platinum button with Ag/AgCl reference 1 point 100 m 2 years for pH/ORP sensor
1 year for pH/ORP sensor module
Dissolved Oxygen Optical luminescence - lifetime method 1 or 2 point 100 m 2 years for optical DO sensor
1 year for optical DO sensor cap
Barometer - 1 point - 3 years, integrated into ProDSS handheld
Conductivity Four nickel electrode cell 1 point 100 m 2 years for conductivity/temperature sensor
Specific Conductance* Calculated from conductivity & temperature - - 1 point
Salinity* Calculated from conductivity & temperature 1 point - -
Total Dissolved Solids (TDS)* Calculated from specific conductance & a user selectable TDS multiplier (0.30 to 1.00; default 0.65) - - -
Resistivity* Calculated from conductivity & temperature - - -
Seawater Density* Sigma is calculated from salinity, temperature & pressure (depth) Sigma T is calculated from salinity & temperature - - -
Turbidity Nephelometric - Optical, 90° scatter 1, 2, or 3 point - 2 years for turbidity sensor
Total Suspended Solids(TSS)* User correlated from turbidity field measurements & lab TSS measurements from grab samples - - -
Ammonium** Ion selective electrode 1, 2, or 3 point 20 m 2 years for ammonium sensor
6 months for ammonium sensor module
Ammonia* Calculated from ammonium, temperature, salinity & pH - - -
Chloride** Ion selective electrode 1, 2, or 3 point 20 m 2 years for chloride sensor
6 months for chloride sensor module
Nitrate** Ion selective electrode 1, 2, or 3 point 20 m 2 years for nitrate sensor
6 months for nitrate sensor module
Depth Pressure transducer 1 point - 2 years, integrated into cable assembly

*Derived/calculated parameter **ISEs for freshwater only; 20 meter maximum depth


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YSI Pro Plus MCERTS certificate EPA compliance certificate Professional Plus Calibration Tips YSI Pro Plus Quick Start Photo Gallery How to store your YSI Pro Plus YSI Display & Logging Removing Bubble in pH Probe Changing a DO Mebrane & Calibrating a YSI Pro Plus Using Flow Cells for Groundwater Sampling

YSI Pro Plus

The YSI Professional Plus handheld multiparameter meter provides extreme flexibility for the measurement of a variety of combinations.

The new Quatro cable attached to the Pro Plus allows you to utilise 4-ports to measure temperature/conductivity, DO, and any two ISEs among pH, ORP, ammonium, chloride, or nitrate.

The Pro Plus instrument meets the demands of true field work. The instrument is rated to IP-67 standards even without the battery cover on. Other tough features include a 3-year warranty, Mil-spec connectors, rubber over moulded case, a 2-year cable warranty and one year probe warranty. In-house testing procedures also include 1-meter drop tests from all angles to ensure expected field-durability.

YSI Pro 20 and ProODO™

The YSI Pro 20 and ProODO series are water proof, rugged, reliable single parameter handheld meters available for the determination of Dissolved Oxygen. The Pro 20 features the YSI Professional Series Galvanic or Polarographic DO sensors whilst the Pro ODO has an Optical DO sensor.

They both include:

- 3-year instrument warranty and a 2-year cable and probe warranty (Pro 20 Probe has 1 year warranty)
- Military Spec (MS) connectors
- Rubber overmolded case
- Field tested cables
- Rugged, weighted probe guard

YSI Pro2030

The YSI Pro2030 is a durable and easy to use handheld dissolved oxygen / conductivity meter that automatically compensates for changes in salinity values. Rugged, easy to use and reliable, this meter will also measure specific conductance, total dissolved solids (TDS), barometric pressure and temperature.

It also benefits from:

- MS (Military Spec) cable connector
- Choice of field DO sensors: Polarographic or Galvanic
- Rugged, weighted field cables available in lengths from 1 to 30 metres
- Being completely waterproof to 1 metre submersion
- 3-year instrument; 2-year cable; 1-year Polarographic/6-month Galvanic sensor warranty
- Storing 50 data sets to ensure data integrity.

YSI Exo Water Quality Logger


The EXO Sonde from Xylem is a multiparameter water quality meter which can measure and log data. The EXO1 in the Van Walt rental stock will be configured to measure and log the following parameters simultaneously: pH, EC, Temperature, Redox, Dissolved Oxygen and Turbidity. When connected to the Storm 3 telemetry unit, additionally, it will also report water level.

The EXO Sondes are very special and the result of a US$ 24 million investment programme. The idea was to create the ultimate water quality measuring device and no shortcuts were taken. The EXO's have a host of features, viewable on the specification sheets but a few are worth focusing on:

  • Wet mateable connectors. By the nature of their intended use, this type of device is rarely dry. This doesn't matter with the EXO's. Probes and cables can be disconnected and reconnected EVEN WHEN WET.
  • The electrodes are made of titanium for robustness and durability
  • Calibration data is stored WITHIN THE ELECTRODES so spares can be pre-calibrated and exchanged on site without the necessity of returning the entire unit back to base for recalibration.

The robust, multiparameter, 4-port EXO offers a wide range of capabilities for groundwater monitoring of:

  • Conductivity and Temperature
  • Optical Dissolved Oxygen
  • pH / ORP
  • Depth (integral)
  • Total Algae (Dual-channel Chlorophyll and Blue-green Algae)
  • Turbidity.


The EXO is smart, cost-effective and adaptable for the future. Its high-impact body is built to record water quality to depths of 250 meters. The data is stored on-board the instrument for downloading to a laptop on completion of the monitoring sequence.

The EXO logger is also available with telemetry.

  • Rugged and easy to use
  • High-accuracy sensors with on-board memory
  • Wireless communications to set-up, calibrate and deploy the instrument
  • Fast response times for profiling and sampling
  • In-built diagnostics to make setting-up and configuration even easier
  • Improved power management to extend deployment times
  • Quick and easy calibration in less than 15 minutes
  • Reliable and accurate with smart controls and guided prompts to reduce the opportunity for errors
  • Smart probes and active port monitoring automatically detects any sensor damage
  • Isolated components so prevents short circuits
  • Wet-mateable connectors that will resist corrosion
  • In built monitoring systems automatically scans for errors, monitors the memory status and continuously verifies the sensor operation to ensure successful deployment
  • Accurate data collection for up to 90 days.

Specifications: YSI Exo Water Quality Logger

EXO1 Specifications
Diameter 4.70 cm (1.85 in)
Length 64.77 cm (25.50 in)
Peripheral Ports 1 power communication port
Sensor Ports 4
Warranty, 1-Year pH, ORP and optical DO membranes
Warranty, 2-Year Cables, sonde bulkhead, handheld and the following sensors: conductivity, temperature, depth and optical sensors
Weight 1.42 kg (3.15 lbs)
General Sonde Specifications
Battery Life 90 days**
Communications Computer Interface: Bluetooth wireless technology (between sonde and handheld or computer with KOR software), RS-485, USB;
Output Options: USB with signal output adapter (SOA); RS-232 & SDI-12 with DCP-SOA.
Data Memory 512 MB total memory; >1,000,000 Logged readings
Depth Rating 0 to 250 m (0 to 820 ft)
Sample Rate Up to 4 Hz
Temperature - Operating -5 to +50°C
Temperature - Storage -20 to +80°C
**Typically 90 days at 20˚C at 15-minute logging interval; temperature / conductivity, pH/ORP, DO, and turbidity sensors installed on EXO1; or temperature/conductivity, pH/ORP, DO, total algae, and turbidity sensors installed with central wiper that rotates once per logging interval on EXO2. Battery life is heavily dependent on sensor configuration. Specifications indicate typical performance and are subject to change. Xenoy is a trademark of SABIC Innovative Plastics IP BV. EXO Bluetooth modules comply with Part 15C of FCC Rules and have FCC, CE Mark and C-tick approval. Bluetooth-type approvals and regulations can be country specific. Check local laws and regulations to insure that the use of wireless products purchased from Xylem are in full compliance. EXO components are not compatible with YSI 6-Series sondes, sensors, or handheld.

Videos, Manuals & Downloads

Introducing the Xylem EXO1 Water Quality Sonde


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Flow-Through Cells

Flow-Through Cells are available for the YSI multi-parameter probe or with cut-outs for generic industry standard electrodes. They are normally used with peristaltic pumps.

Calibration Buffers

Calibration Buffers are necessary for calibration and checking water quality meters. We offer exceptionally well priced reagents by Reagecon. As expected these are hallmarked.

WTW pH Data Logger


Designed for long term, continuous pH surface and groundwater monitoring in challenging and difficult to access locations where a large quantity of reliable data is required.

Delivers stable, accurate measurements.

Is usually supplied pre-programmed to start at a specified time and the data is retrieved by Van Walt and supplied in CSV format.


  • Intelligent energy management for longer battery lifetime
  • Up to 600,000 data records
  • 25mm diameter for both ground and surface water monitoring
  • USB connection for fast data transfer to PC
  • Replaceable pH electrode
  • Integrated temperature sensor
  • User-friendly software interface
  • LED status light provides information on memory and measurement operation
  • Quick start button to better control pH measurements
  • Fully backed by the Van Walt Technical team.

Specifications: WTW pH Data Logger

WTW pH Data Logger
pH Range * 0.000 to 20.000
mV Range * -1000.0 to +1000.0
Temperature Range * 23 to 221°F (-5.0 to +105.0°C)
pH Resolution 0.001
mV Resolution 0.1 mV
Temperature Resolution 0.1°F (0.1°C)
pH Accuracy * < 0.005 +1 Digit
mV Accuracy * < 0.2mV +1 Digit
Temperature Accuracy * < 0.1°F (0.1°C) +1 Digit
Temperature sensor Automatic recognition of the temperature sensor of the electrode: NTC 30 (30 kΩ at 25 °C / 77 °F) or Pt1000
Temperature Compensation Automatic
Calibration Automatic buffer detection
Measuring Medium:
Temp Range
pH Range

32 to 140 °F (0 to 60 °C)
2 to 12
Data Volume up to 600,000 data records
Sampling Interval adjustable: 1,5,10,30 s/ 1,5,10,15,30 min/ 1,2,3,6,9,12,24 hr
Power Supply Lithium ion battery (3.6V, AA size, 2600 mAh)
Battery Life Up to 16 months depending on the sample rate
USB Interface Type USB 1.1, USB-B (Device), data output
Protection Rating IP 68
Maximum Pressure/Depth 145 PSI (10 bar)/328 ft (100 m)
Storage Temperature -13 to 149°F (-25 to +65°C)
Material Metal parts (Stainless steel 1.4571**), Battery Compartment (Brass, gold-plated)
Size of Probe 0.98 inch Diameter x 15.83 inch L (25 mm dia. x 402 mm long), retaining hole 0.26 inch (6.5mm)
Weight 1.9 lb. (860 g) including electrode
Certificates CE
* The measuring ranges and accuracy exclusively refer to the measuring electronics of the pH datalogger without the electrode. For the measuring ranges and accuracy of the operable pH datalogger, the specifications of the electrode and buffer solutions have also to be taken into account. ** Stainless steel can be susceptible to corrosion at chloride concentrations of >500 mg/l.

pH SensoLyt Electrode

pH Range 2.000 to 12.000
Referenece Electrolyte Polymer, AgCl free
Junction Single hole junction
Shunt Element Ag/AgCl
Temp Range 32 to 140°F (0 to 60°C)
Membrane Resistance at 25°C < 500 MOhm
Maximum Pressure/Depth 145 PSI (10 bar)/328 ft (100 m)
Connection SMEK head, 6-pole
Material Shaft: Glass, O-rings: FPM (Viton), SMEK plug: PEEK with gold plated contacts
Dimensions 4.7 inch L x 1/2 inch Dia (120 mm L x 12 mm Dia)
Weight 1.6 oz (45 g)

Videos, Manuals & Downloads


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Water Quality Testing Equipment you can trust

For field use YSI Water Quality Meters have an established track record. Rugged, reliable, accurate – this equipment has all the attributes a water quality meter should possess. Quite simply the benchmark for what a field water quality meter should be.

Our range of water quality and water level meters can be used for sampling, monitoring and logging results for surface water applications in canals, streams, rivers, wetlands and estuaries. Our telemetry, sensors and water level loggers form a powerful monitoring system, which is able to generate event specific alarms like flood alerts, if required.

For the rigours of field use only the most rugged, accurate, reliable and flexible solutions are an option. After almost a decade of experience, for us, only YSI Water Quality Meters make the grade.

Water Quality Monitoring Options